Ketosis-prone type 2 diabetes (KPD) is characterized by male predominance, onset at a young age, obesity, and sudden onset of diabetic ketosis/ketoacidosis without precipitating factors, negative anti-islet autoantibodies, and β-cell function preservation after recovery from diabetic ketosis/ketoacidosis following temporal insulin therapy. This evidence concerns the gene INS and obesity due to melanocortin 4 receptor deficiency.